LIBREVILLE (Reuters) - Gabon opposition leader Jean Ping on Saturday rejected what he said was an "unjust" ruling by the Constitutional Court which upheld the victory of President Ali Bongo in the Aug. 27 poll that he says was tarnished by fraud.

The refusal by Ping, who says he won the presidential poll, to accept the court ruling raises the prospect of a potentially violent political crisis in the central African oil producer.

The court had agreed to Ping's petition to re-examine results in Haut-Ogooue province, where Bongo was declared to have won 95 percent on a turnout of 99.9 percent.

However, in a ruling late on Friday, it refused to accept copies of vote tally sheets provided as evidence by Ping, stating he had failed to prove their authenticity.

Speaking to supporters and reporters at his residence in the capital Libreville, Ping called for people to "remain vigilant and mobilized".

"We will ensure the choice of the Gabonese people is respected. 2016 will not be 2009," Ping said.

Ali Bongo came to power in a contentious 2009 election following the death of his father Omar Bongo, who was president of Gabon for 42 years.

Ping, a lifelong political insider in Gabon who has also served as chairman of the African Union Commission, was a close ally of Omar Bongo.

President Ali Bongo sought to ease tensions on Saturday, calling for dialogue and promising a new inclusive government.

"I look forward to inviting members of all political parties to join our efforts and come with us to the Cabinet," he told Reuters in an interview.

He said the new government would "most likely" include leading opposition figures and did not rule out the possibility of reserving a place for Ping.

However, he rejected the option of international mediation.

"We don't need international mediation. Among Gabonese, we know how to talk to each other," he said.

POLL INTEGRITY IN DOUBT

Gabon's government was placed under renewed international pressure when the European Union complained on Saturday that its elections observer mission had been granted "very limited access" to the court's review of results.

"Consequently, the Gabonese people's confidence in the integrity of the electoral process can, legitimately, be put in doubt," High Representative for Foreign Affairs Federica Mogherini and Development Commissioner Neven Mimica said in a statement.

The foreign ministry of former colonial power France echoed the EU, saying in a statement that the court's examination of the results did not "remove all doubt".

Chad's president, Idriss Deby, the African Union's current chairman, meanwhile duly noted the court decision and called upon Bongo to create the necessary conditions for fruitful dialogue.

"(Deby) urges the political opposition to demonstrate more responsibility and privilege dialogue and consultation," said a statement released by Chad's presidency.

The A.U. had dispatched a team of judges to monitor the work of the Constitutional Court.

Six people were killed earlier this month in riots that followed the interior minister's declaration of Bongo as winner of the poll by fewer than 6,000 votes.

The opposition claims up to 100 people died.

Trucks full of police and soldiers were positioned at crossroads and roundabouts across the capital from early morning on Saturday. However, there were no reports of protests.

"I'm glad there is no war. We need the politicians to talk," said Arnel Sama, 40, an unemployed resident of Libreville.

Bongo had entered a counter-claim with the constitutional court accusing Ping of fraud.

The court canceled results from 21 polling stations in Libreville over irregularities, helping Bongo to improve his margin of victory from 49.85 percent of ballots cast to 50.66 percent in the final court-certified result.

(Additional reporting by Mathieu Rosemain in Paris and Madjiasra Nako in N'Djamena; Writing by Joe Bavier; Editing by Andrew Bolton and Matthew Lewis)